Hydraulic excavators comprise an upper unit rotatably mounted on a tracked undercarriage or car body for selectively positioning a work implement during excavator operation. A lock pin, mounted exteriorly of a swing gear mechanism for selectively rotating the upper unit, is normally mounted on the upper unit to engage the undercarriage to lock the upper unit in position, particularly during transport of the excavator to a remote job site. The pin is thus exposed to damage and must be actuated manually.